#![allow(unused_imports)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;
use std::ops::Bound::*;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn get_idx(i: usize, x: usize, y: usize, w: usize) -> usize {
    i + x * 2 + y * 2 * w
}

fn main() {
    let v = read_vec::<usize>();
    let (n, m) = (v[0], v[1]);
    let mut cost_dict = HashMap::new();
    for i in 0..m {
        let v = read_vec::<i64>();
        let (h, w, c) = (v[0] as usize - 1, v[1] as usize - 1, v[2]);
        cost_dict.insert((h, w), c);
    }

    let mut edges = vec![vec![]; n * n * 2];
    for y in 0..n {
        for x in 0..n {
            let cost;
            let cur0 = get_idx(0, x, y, n);
            let cur1 = get_idx(1, x, y, n);
            if cost_dict.contains_key(&(y, x)) {
                cost = cost_dict[&(y, x)];
            } else {
                cost = 0;
            }
            for (adj_x, adj_y) in get_adjacents(x, y, n, n) {
                let adj0 = get_idx(0, adj_x, adj_y, n);
                let adj1 = get_idx(1, adj_x, adj_y, n);

                edges[adj0].push((cur0, cost + 1));
                edges[adj1].push((cur1, cost + 1));
                edges[adj0].push((cur1, 1));
            }
        }
    }
    let d = solve(&edges, 0);
    let ans = d[get_idx(1, n - 1, n - 1, n)];
    println!("{}", ans);
}

fn get_adjacents(x: usize, y: usize, w: usize, h: usize) -> Vec<(usize, usize)> {
    let mut adjacents = vec![];
    if x > 0 {
        adjacents.push((x - 1, y));
    }
    if y > 0 {
        adjacents.push((x, y - 1));
    }
    if y < h - 1 {
        adjacents.push((x, y + 1));
    }
    if x < w - 1 {
        adjacents.push((x + 1, y));
    }
    adjacents
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

const INF: i64 = 100000_00000_00000;

fn solve(edges: &Vec<Vec<(usize, i64)>>, start_idx: usize) -> Vec<i64> {
    let num_apexes = edges.len();
    let mut d = vec![INF; num_apexes];
    d[start_idx] = 0;
    let mut que = std::collections::BinaryHeap::new();
    que.push((std::cmp::Reverse(0), start_idx));

    while let Some((u, v)) = que.pop() {
        if d[v] < u.0 {
            continue;
        }
        for e in &edges[v] {
            if d[v] != INF && d[e.0] > d[v] + e.1 {
                d[e.0] = d[v] + e.1;
                que.push((std::cmp::Reverse(d[e.0]), e.0));
            }
        }
    }
    d
}